The rotational speed for the timer processor unit (TPU) level is determined in two different ways according to the related art. First, the TPU calculates the rotational speed based on the last tooth time and second, the TPU receives a tooth time from the functional level of the control unit. The tooth time is calculated based on the segment time. In an internal combustion engine having six cylinders, for example, one segment includes 720/6 crank angles, i.e., crankshaft angles of 120°.
According to the related art, the rotational speed of the crankshaft and thus of the engine is determined between two consecutive tooth flanks. Thus, the period of time is measured which has elapsed between two consecutive tooth flanks, the crankshaft angle between consecutive tooth flanks being known. Hence, the engine speed may be directly determined.
The method according to the related art has the disadvantage that, by forming the tooth time from the segment time, considerable errors occur in the dynamics in the low rotational speed range, while, in direct tooth time analysis, the tolerances in the position and the development of the tooth flanks have a strong effect on the accuracy of the rotational speed determination at high speeds during steady-state operation.
Therefore, it is an object of the present invention to increase the accuracy of the rotational speed determination.